CBSE Class 9 Science Chapter 6 'Tissues' Notes

Introduction:

Welcome to our online tutorial classes, where learning meets innovation! In this segment, we embark on an exciting journey into the realm of matter with our meticulously crafted CBSE Class 9 Science Chapter 6 notes on “Tissues”. Through these notes, we aim to ignite your curiosity, deepen your understanding, and empower you with knowledge that transcends the boundaries of the classroom.

Chapter 6, ‘Tissues’, in CBSE Class 9 Science, explores the types and functions of tissues in plants and animals. It covers simple and complex plant tissues like parenchyma, collenchyma, sclerenchyma, xylem, and phloem, and animal tissues including epithelial, connective, muscular, and nervous tissues, providing examples and detailed explanations.

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CBSE class 9 Science Chapter 6 ‘Tissues’ Overview

CBSE Class 9 Science Chapter 6, ‘Tissues’, explores the concept of tissues, their types, and functions in both plants and animals. It begins with an introduction to tissues, explaining how they provide efficiency in multicellular organisms. The chapter then delves into plant tissues, distinguishing between simple and complex tissues, and detailing their specific types such as parenchyma, collenchyma, sclerenchyma, xylem, and phloem. The chapter also discusses animal tissues, including epithelial, connective, muscular, and nervous tissues. It elaborates on the structure and function of each tissue type, providing examples like blood, bone, and neurons. The chapter includes activities and exercises to reinforce understanding. Overall, it provides a comprehensive understanding of how different tissues contribute to the structure and function of living organisms.

With our expertly curated notes, you’ll be well-equipped to ace your CBSE Class 9 Science exams and embark on a lifelong journey of discovery and learning.

CBSE class 9 Science Chapter 6 ‘Tissues’ Notes

Cellular Organization

All living organisms are made of cells.
In unicellular organisms like Amoeba, a single cell performs all basic functions such as movement, intake of food, gaseous exchange, and excretion.
In multicellular organisms, there are millions of cells, most of which are specialized to carry out specific functions.
Each specialized function is taken up by a different group of cells, allowing them to perform their function very efficiently.

Tissues

Cells specializing in one function are often grouped together in the body, forming a tissue.
A group of cells that are similar in structure and/or work together to achieve a particular function forms a tissue.
Examples of tissues include blood, phloem, and muscle.

Differences Between Plant and Animal Tissues

Plants are stationary and have a large quantity of supportive tissue, generally containing dead cells.
Animals move around in search of food, mates, and shelter, consuming more energy than plants. Most of their tissues are living.
The growth in plants is limited to certain regions, while this is not so in animals.
Plant tissues can be classified as growing (meristematic) tissue and permanent tissue based on their dividing capacity.
Cell growth in animals is more uniform, so there is no such demarcation of dividing and non-dividing regions in animals.
The structural organization of organs and organ systems is far more specialized and localized in complex animals than in very complex plants.
This fundamental difference reflects the different modes of life pursued by these two major groups of organisms, particularly in their different feeding methods.
They are differently adapted for a sedentary existence on one hand (plants) and active locomotion on the other (animals), contributing to this difference in organ system design.

Plant Tissues

Meristematic Tissue

The growth of plants occurs only in certain specific regions due to the presence of dividing tissue, also known as meristematic tissue.
Meristematic tissues are classified as apical, lateral, and intercalary depending on the region where they are present.
Apical meristem is present at the growing tips of stems and roots and increases the length of the stem and the root.
The girth of the stem or root increases due to lateral meristem (cambium).
Intercalary meristem seen in some plants is located near the node.
Cells of meristematic tissue are very active, have dense cytoplasm, thin cellulose walls, and prominent nuclei. They lack vacuoles.

Permanent Tissue

Cells formed by meristematic tissue take up a specific role and lose the ability to divide, forming a permanent tissue.
This process of taking up a permanent shape, size, and function is called differentiation.
Differentiation leads to the development of various types of permanent tissues.

Section of a Stem for CBSE Class 7 Science Chapter 6 Tissues by Online Tutorial Classes — *Section of a Stem*

Simple Permanent Tissue

A few layers of cells beneath the epidermis are generally simple permanent tissue.

Types of simple tissues for CBSE Class 7 Science chapter 6 Tissues by Online Tutorial Classes — *Various types of simple tissues*

Parenchyma

Most common simple permanent tissue.
Consists of relatively unspecialized cells with thin cell walls.
Usually loosely arranged, thus large spaces between cells (intercellular spaces) are found in this tissue.
Generally stores food.
In some situations, it contains chlorophyll and performs photosynthesis, and then it is called chlorenchyma.
In aquatic plants, large air cavities are present in parenchyma to help them float. Such a parenchyma type is called aerenchyma.

Collenchyma

Provides flexibility in plants.
Allows bending of various parts of a plant like tendrils and stems of climbers without breaking.
Also provides mechanical support.
Found in leaf stalks below the epidermis.
Cells of this tissue are living, elongated, and irregularly thickened at the corners. There is very little intercellular space.

Sclerenchyma

Makes the plant hard and stiff.
Cells of this tissue are dead. They are long and narrow as the walls are thickened due to lignin.
Often these walls are so thick that there is no internal space inside the cell.
Present in stems, around vascular bundles, in the veins of leaves, and in the hard covering of seeds and nuts.
Provides strength to the plant parts.

Epidermis

The outermost layer of cells, usually made of a single layer of cells.
In some plants living in very dry habitats, the epidermis may be thicker since protection against water loss is critical.
The entire surface of a plant has an outer covering of epidermis. It protects all the parts of the plant.
Epidermal cells on the aerial parts of the plant often secrete a waxy, water-resistant layer on their outer surface. This aids in protection against loss of water, mechanical injury, and invasion by parasitic fungi.
Cells of epidermal tissue form a continuous layer without intercellular spaces. Most epidermal cells are relatively flat. Often their outer and side walls are thicker than the inner wall.
Small pores here and there in the epidermis of the leaf are called stomata. Stomata are enclosed by two kidney-shaped cells called guard cells. They are necessary for exchanging gases with the atmosphere. Transpiration (loss of water in the form of water vapor) also takes place through stomata.
Epidermal cells of the roots, whose function is water absorption, commonly bear long hair-like parts that greatly increase the total absorptive surface area.
In some plants like desert plants, epidermis has a thick waxy coating of cutin (chemical substance with waterproof quality) on its outer surface.
As plants grow older, the outer protective tissue undergoes certain changes. A strip of secondary meristem located in the cortex forms layers of cells which constitute the cork. Cells of cork are dead and compactly arranged without intercellular spaces.

Complex Permanent Tissue

Complex tissues are made of more than one type of cells. All these cells coordinate to perform a common function.

Complex Tissues for CBSE Class science Chapter 5 Tissues by Online Tutorial Classes — *Types of complex tissue*

Xylem and Phloem

Xylem and phloem are examples of complex tissues. They are both conducting tissues and constitute a vascular bundle.
Vascular tissue is a distinctive feature of the complex plants, one that has made possible their survival in the terrestrial environment.

Xylem

Xylem consists of tracheids, vessels, xylem parenchyma, and xylem fibres.
Tracheids and vessels have thick walls, and many are dead cells when mature.
Tracheids and vessels are tubular structures. This allows them to transport water and minerals vertically.
The parenchyma stores food. Xylem fibres are mainly supportive in function.

Phloem

Phloem is made up of five types of cells: sieve cells, sieve tubes, companion cells, phloem fibres, and the phloem parenchyma.
Sieve tubes are tubular cells with perforated walls.
Phloem transports food from leaves to other parts of the plant. Except phloem fibres, other phloem cells are living cells.

Animal Tissues

Specialised cells called muscle cells result in movement through their contraction and relaxation.
Oxygen inhaled during breathing is absorbed in the lungs and then is transported to all the body cells through blood.
Blood flows and carries various substances from one part of the body to the other. For example, it carries oxygen and food to all cells. It also collects wastes from all parts of the body and carries them to the liver and kidney for disposal.
Blood and muscles are both examples of tissues found in our body.
On the basis of the functions they perform, different types of animal tissues can be identified, such as epithelial tissue, connective tissue, muscular tissue, and nervous tissue.
Blood is a type of connective tissue, and muscle forms muscular tissue.

Epithelial Tissue

The covering or protective tissues in the animal body are epithelial tissues.
Epithelium covers most organs and cavities within the body and forms a barrier to keep different body systems separate.
The skin, the lining of the mouth, the lining of blood vessels, lung alveoli, and kidney tubules are all made of epithelial tissue.
Epithelial tissue cells are tightly packed and form a continuous sheet. They have only a small amount of cementing material between them and almost no intercellular spaces.
Anything entering or leaving the body must cross at least one layer of epithelium.
The permeability of the cells of various epithelia plays an important role in regulating the exchange of materials between the body and the external environment and also between different parts of the body.
Regardless of the type, all epithelium is usually separated from the underlying tissue by an extracellular fibrous basement membrane.
Different epithelia show differing structures that correlate with their unique functions.

Simple Squamous Epithelium

In cells lining blood vessels or lung alveoli, where transportation of substances occurs through a selectively permeable surface, there is a simple flat kind of epithelium.
Simple squamous epithelial cells are extremely thin and flat and form a delicate lining.
The oesophagus and the lining of the mouth are also covered with squamous epithelium.

The skin, which protects the body, is also made of squamous epithelium.
Skin epithelial cells are arranged in many layers to prevent wear and tear. Since they are arranged in a pattern of layers, the epithelium is called stratified squamous epithelium.

Columnar Epithelium

Where absorption and secretion occur, as in the inner lining of the intestine, tall epithelial cells are present.
This columnar epithelium facilitates movement across the epithelial barrier.
In the respiratory tract, the columnar epithelial tissue also has cilia, which are hair-like projections on the outer surfaces of epithelial cells. These cilia can move, and their movement pushes the mucus forward to clear it. This type of epithelium is thus ciliated columnar epithelium.

Cuboidal Epithelium

Cuboidal epithelium forms the lining of kidney tubules and ducts of salivary glands, where it provides mechanical support.
Epithelial cells often acquire additional specialisation as gland cells, which can secrete substances at the epithelial surface.
Sometimes a portion of the epithelial tissue folds inward, and a multicellular gland is formed. This is glandular epithelium.

Connective Tissue

Connective tissues have cells that are loosely spaced and embedded in an intercellular matrix. The matrix may be jelly-like, fluid, dense, or rigid.
The nature of the matrix differs in concordance with the function of the particular connective tissue.

Blood

Blood is a type of connective tissue.
Blood has a fluid matrix called plasma, in which red blood corpuscles (RBCs), white blood corpuscles (WBCs), and platelets are suspended.
The plasma contains proteins, salts, and hormones.
Blood flows and transports gases, digested food, hormones, and waste materials to different parts of the body.

Bone

Bone is another example of a connective tissue.
It forms the framework that supports the body, anchors the muscles, and supports the main organs of the body.
Bone cells are embedded in a hard matrix that is composed of calcium and phosphorus compounds.

Ligament and Tendon

Two bones can be connected to each other by another type of connective tissue called the ligament. Ligaments contain very little matrix and connect bones with bones.
Tendons connect muscles to bones and are another type of connective tissue. Tendons are fibrous tissue with great strength but limited flexibility.

Cartilage

Cartilage has widely spaced cells. The solid matrix is composed of proteins and sugars.
Cartilage smoothens bone surfaces at joints and is also present in the nose, ear, trachea, and larynx.

Areolar Connective Tissue

Areolar connective tissue is found between the skin and muscles, around blood vessels and nerves, and in the bone marrow.
It fills the space inside the organs, supports internal organs, and helps in the repair of tissues.

Adipose Tissue

Fat-storing adipose tissue is found below the skin and between internal organs.
The cells of this tissue are filled with fat globules. Storage of fats also lets it act as an insulator.

Muscular Tissue

Muscular tissue consists of elongated cells, also called muscle fibers. This tissue is responsible for movement in our body.
Muscles contain special proteins called contractile proteins, which contract and relax to cause movement.

Voluntary Muscles

We can move some muscles by conscious will. Such muscles are called voluntary muscles.
These muscles are also called skeletal muscles as they are mostly attached to bones and help in body movement.
Under the microscope, these muscles show alternate light and dark bands or striations when stained appropriately. As a result, they are also called striated muscles.
The cells of this tissue are long, cylindrical, unbranched, and multinucleate (having many nuclei).

Involuntary Muscles

The movement of food in the alimentary canal or the contraction and relaxation of blood vessels are involuntary movements.
Smooth muscles or involuntary muscles control such movements. They are also found in the iris of the eye, in ureters, and in the bronchi of the lungs.
The cells are long with pointed ends (spindle-shaped) and uninucleate (having a single nucleus). They are also called unstriated muscles.

Cardiac Muscles

The muscles of the heart show rhythmic contraction and relaxation throughout life. These involuntary muscles are called cardiac muscles.
Heart muscle cells are cylindrical, branched, and uninucleate.

Nervous Tissue

All cells possess the ability to respond to stimuli. However, cells of the nervous tissue are highly specialized for being stimulated and then transmitting the stimulus very rapidly from one place to another within the body.
The brain, spinal cord, and nerves are all composed of the nervous tissue.
The cells of this tissue are called nerve cells or neurons. A neuron consists of a cell body with a nucleus and cytoplasm, from which long thin hair-like parts arise.
Usually each neuron has a single long part (process), called the axon, and many short, branched parts (processes) called dendrites. An individual nerve cell may be up to a meter long.
Many nerve fibers bound together by connective tissue make up a nerve.
The signal that passes along the nerve fiber is called a nerve impulse. Nerve impulses allow us to move our muscles when we want to.
The functional combination of nerve and muscle tissue is fundamental to most animals. This combination enables animals to move rapidly in response to stimuli.

Important Points

Tissue is a group of cells similar in structure and function.
Plant tissues are of two main types – meristematic and permanent.
Meristematic tissue is the dividing tissue present in the growing regions of the plant.
Permanent tissues are derived from meristematic tissue once they lose the ability to divide. They are classified as simple and complex tissues.
Parenchyma, collenchyma and sclerenchyma are three types of simple tissues. Xylem and phloem are types of complex
tissues.
Animal tissues can be epithelial, connective, muscular and nervous tissue.
Depending on shape and function, epithelial tissue is classified as squamous, cuboidal, columnar, ciliated and glandular.
The different types of connective tissues in our body include areolar tissue, adipose tissue, bone, tendon, ligament,
cartilage and blood.
Striated, unstriated and cardiac are three types of muscle tissues.
Nervous tissue is made of neurons that receive and conduct impulses.

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